There has been an increasing number of an electrophotographic image forming apparatus structured so that a unit (which hereafter will be referred to as process cartridge), which is a cassette in which image formation components are integrally disposed, is removably installable in the main assembly of the apparatus, in order to make it easier to maintain an electrophotographic image forming apparatus.
Many of the process cartridges usable with the abovementioned electrophotographic image forming apparatuses employ a charge roller as a charging member, and are structured to place the charge roller in contact with a photosensitive member to charge the photosensitive member. Further, a substantial number of process cartridges which employ a charge roller are structured so that the charge roller is kept pressed upon the peripheral surface of their photosensitive member with the use of springs or the like in order to keep stable the charge nip between the peripheral surface of the charge roller and that of the photosensitive member.
However, if a charge roller is continuously kept pressed upon a photosensitive member from when a process cartridge is shipped out of a process cartridge factory (when process cartridge is completed) to when the cartridge is used for the first time, the charge roller will become deformed. Obviously, the usage of a deformed charge roller for image formation results in the formation of an unsatisfactory image.
One of the conceivable means for dealing with the above-described problem is to structure a process cartridge so that a spacer is placed between its charge roller and photosensitive member. It has been common practice to structure a process cartridge so that before the process cartridge is installed in the main assembly of an image forming apparatus by a user, the spacer is removed by the user to place the charge roller in contact with the photosensitive drum. However, from the standpoint of usability, it is desired that a process cartridge is structured so that as the process cartridge is installed into the main assembly of an image forming apparatus, its spacer which has kept the charge roller separated from the photosensitive drum is retracted by the force which the spacer receives from the main assembly of the apparatus.
For example, Japanese Laid-open Patent Application 2003-76117 discloses a process cartridge which has a spacer for keeping a charge roller separated from a photosensitive drum, and which is structured so that in order to allow the photosensitive member and charge roller to be placed in contact with each other, the spacer is rotationally movable about the shaft of the charge roller by the force which the spacer receives from the main assembly of the image forming apparatus.
It is desired that a charge roller is kept pressed upon a photosensitive drum to keep the charge nip stable during an image forming operation. This is true for a process cartridge structured so that its charge roller and photosensitive member are kept separated from each other by its spacer until it is installed in the main assembly of an image forming apparatus for the first time. For example, in the case of the process cartridge disclosed in the aforementioned Japanese Laid-open Patent Application 2003-76117, the cartridge is structured so that the bearings for the shaft of the charge roller, which are independent from the spacer, are kept pressed toward the photosensitive drum with the use of springs in order to keep the charge nip stable.
However, placing the bearing which bears the force for keeping the charge roller pressed toward the photosensitive member while bearing the shaft of the charge roller as disclosed in Japanese Laid-open Patent Application 2003-76117, and the spacer, side by side in terms of the lengthwise direction of the charge roller requires a process cartridge to be increased in length.
One of the conceivable solutions to the above described problem is to integrate the bearing which bears the force for keeping the charge roller pressed toward the photosensitive member while bearing the shaft of the charge roller, with the spacer.
However, in the case of a process cartridge structured so that its spacer which is rotationally movable about the shaft of the charge roller is given the force for allowing the charge roller to be placed in contact with the photosensitive drum of the cartridge and keeping the charge roller in contact with the photosensitive drum thereafter, it was difficult to keep stable the force for keeping the charge roller in contact with the photosensitive member after the rotational movement of the spacer. That is, the above described structural arrangement for a process cartridge is problematic in that the pressure applying members for applying pressure to the spacers after the rotational movement of the spacer about the shaft of the charge roller, which is caused by the force from the main assembly of the image forming apparatus, is made to be unstable in attitude by the rotation of the spacer.